Chemical Clock
A simulation of the Belousov-Zhabotinsky oscillating reaction. The Oregonator model drives periodic switching between two chemical states, visible as the beaker alternates between blue and orange while the concentration time series scrolls in real time.
About this lab
The Belousov-Zhabotinsky (BZ) reaction is the most famous example of a chemical oscillator — a far-from-equilibrium reaction in which concentrations of intermediates periodically rise and fall. First observed by Boris Belousov in the 1950s, it was initially dismissed as an error because the Second Law of Thermodynamics was wrongly thought to forbid such behavior. In fact, the oscillation is entirely thermodynamic: the system is driven by an overall free-energy decrease while intermediate species cycle through recurring states.
The Oregonator, developed by Field, Koros, and Noyes at the University of Oregon in 1972, is a simplified three-variable ODE model that captures the essential dynamics of the BZ reaction. The variables represent the concentrations of bromous acid (HBrO2), bromide ion (Br-), and the oxidized form of the metal catalyst (Ce4+ or ferriin). The model exhibits a limit cycle: after transients die out, the concentrations trace a stable periodic orbit regardless of initial conditions.
In this simulation, the color of the beaker represents the oxidation state of the catalyst. When the catalyst is in its oxidized form (high z), the solution appears blue (as with ferroin indicator); when reduced, it turns orange. The scrolling time-series plot shows the concentrations of the Oregonator variables, letting you see the sharp autocatalytic bursts of bromous acid that drive each oscillation cycle.